Conventionally, batteries (so-called secondary cells) have been used as a power supply source for an electric car. Examples of batteries include the battery packs discussed in Patent Literature 1 and 2.
Recent years have seen the advent of a system for loaning out a plurality of batteries to users of electric cars. With this system, a battery is loaned out to a system user, and a returned battery is exchanged (swapped) with a charged battery when the used battery is returned from the user. This system is therefore called a battery swap system.